Lithium oxyhalide battery separator material

ABSTRACT

Methods for producing ceramic films Yttria Stabilized Zirconia (3YSZ) and aluminum titanate (Al2TiO5), and the physical properties of these films are described. The films produced have thicknesses and integrity suitable for handling and corrosion resistance to electrolytes, porosity, ion permeability and electrical resistivity suitable for use as separators between positive and negative layers for forming electrical batteries, particularly lithium batteries.

This invention was made with Government support under HQ0147-16-C-7018, awarded by the US Missile Defense Agency. The US Government has certain rights in the inventions described herein.

BACKGROUND

There is a need to decrease downtime and increase lifetime and safety of batteries installed in systems that are inactive for long periods of time but must be maintained in a standby status for rapid deployment. For example, lithium oxyhalide batteries (LOHB) and potentially other Lithium-based batteries used in such systems include separators made of microporous polytetrafluoroethylene (PTFE) or glass fiber materials. These separators are expensive and their lifetime and safety is limited.

SUMMARY

High quality ceramic, rollable separators (CeRollS™) described herein, which are designed to replace currently used battery separators, demonstrate improved performance and lower cost as a result, in part, of increasing operational lifetime. LOHB separators are required to: (a) electrically isolate electrodes, (b) be ion permeable, (c) withstand corrosive electrolytes, (d) be suitable for a production environment, including mechanical flexibility and handling, (e) maximize volumetric efficiency for electrolyte capacity, (f) extend shelf life, and (g) optimize efficient electrolyte flow and distribution when the battery is activated, thereby minimizing overall cost. CeRollS can be used with existing PTFE and glass separators as an additional layer, with even greater safety, reliability and useable life. However, this combination with the glass and PTFE separators does increase the thickness of the battery.

Applicant has demonstrated that the CeRollS technology described herein meets performance standards at an electrochemical cell level. Further, the described CeRollS material shows an increased corrosion resistance to thionyl chloride and sulfuryl chloride while being flexible.

Described herein are:

-   -   Successful fabrication of a new battery separator including tape         casting and firing to form a flexible ceramic (Al₂TiO₅)         separator material,     -   Demonstrated superior corrosion resistance to thionyl chloride,         12N hydrochloric acid (HCl) and sulfuryl chloride while two         commercially available separator materials failed the same test.     -   Demonstrated enhanced durability of the CeRollS separators while         remaining intact after >89—days in 12N HCl, >277 days in thionyl         chloride, and >277 days in sulfuryl chloride.     -   Superior permeability characteristics demonstrated by better         ionic permeability than commercial separator materials: Two         different Al₂TiO₅ products produced as described herein showed         an ion permeability of ˜1.16×10⁻¹⁵ cm²/sec. and ˜1.75×10⁻¹⁵         cm²/sec; the first of the two Al₂TiO₅ products having the more         desirable ion permeability.     -   Enhanced electrical resistivity of >5.4×10⁸ Ohm-cm. compared to         literature limits of 10¹⁴ Ohm-cm).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A shows a battery incorporating features of the invention said battery having broad applications in any environment requiring a battery with long term stability.

FIG. 1B is an enlarged view, a cut-away view of the battery of FIG. 1A, the device referred to CeRollS for Lithium battery applications.

FIG. 1C is a further cut-away, enlarged view of the battery of FIGS. 1A and 1B.

FIGS. 2A and 2B show two examples of pieces of Al₂TiO₅ films after firing at 1500° C.

FIGS. 3A-3C illustrate corrosion testing in thionyl chloride where 3A shows Celgard® to be transparent after 15 days but not completely dissolved in the 99% thionyl chloride electrolyte (<1 wt % loss); 3B shows ManniGlas 1200 with a lack of integrity after 15 days and 3C shows an Al₂TiO₅ CeRollS to be intact after 15 days.

FIGS. 4A-4C. shows cyclic voltammetric profiles taken under identical aqueous electrolyte conditions for comparison of ion permeability for Celgard, (4A) ManniGlas® 1200 (4B), and Al₂TiO₅ CeRollS (4C).

FIG. 5A. is a scanning electron microscopy (SEM) image of Al₂TiO₅ at low magnification (500×), showing no agglomerates.

FIG. 5B is a scanning electron microscopy (SEM) image of Al₂TiO₅ at high magnification (2,000×) showing ultimate particle size of ˜15-30 μm.

FIG. 6A is an SEM image of Al₂TiO₅ from a second source at a magnification of 2,000× which shows a few agglomerates.

FIG. 6B is an SEM image of Al₂TiO₅ from the second source at a higher magnification (5,000×) showing ultimate particle size of ˜5-20 μm.

FIG. 7A. is an SEM image of 3YSZ at a first magnification (5,000×) showing agglomerates.

FIG. 7B is an SEM image of 3YSZ at a higher magnification (100,000×) showing particle sizes of ˜40 nm.

FIG. 8A shows the X-Ray diffraction spectrum for Al₂TiO₅ from a first source (SA).

FIG. 8B shows the X-Ray diffraction spectrum for Al₂TiO₅ from a second source (AE). The spectra shown in FIGS. 8A and 8B are essentially the same. The major peaks correspond to the known Al₂TiO₅ d-spacing are 4.70, 3.35, 2.65, and 1.90.

FIG. 9A shows the X-Ray diffraction pattern for the 3YSZ used herein.

FIG. 9B shows a literature scan for 3YSZ., this pattern being in close agreement for the major peaks with FIG. 9A.

FIGS. 10A and 1013 are images shown in J. Mater. Sci. (2011) 46:1211-1219: for 50-150 μm granules, with the particles being 0.1 to 1.5 μm. FIGS. 10C and 10D show the Al₂TiO₅ powders used herein;

FIG. 11A shows the ball mill jar used for milling the Al₂TiO₅ to obtain the desired microstructure for a tape slip.

FIG. 11B shows the ball mill jar after milling the Al₂TiO₅ for prepare tape casting slip.

FIG. 11C shows the final container containing the initial tape casting material (Referred to as “slip.”)

FIG. 12A shows a commercial small-scale tape casting head, Al₂TiO₅ milled slip in a de-airing jar bottle, and glass substrate with casting guide rails.

FIG. 12B shows a wet cast tape sample illustrating that some of the initial 14 formulations had issues with cast uniformity.

FIG. 13A shows a dried Al₂TiO₅ tape (Sample 062016RW3091-2).

FIG. 13B shows an improved dried tape placed on a light box for inspection for pinholes. The tape is smooth and without any large pinholes.

FIGS. 14A and 14B show three strips of 062016RW3092-2 (Al₂TiO₅) tape. The Figures show 1 layer with no pressing, 2 pressed layers, and 3 pressed layers respectively. Samples in 14A are unfired and in 14B are fired at 1500° C. for 8 hours.

FIGS. 15A, 15B and 15C show Al₂TiO₅, formulation 072716RW3091-1 where 15A is as cast: FIG. 15B illustrates an unfired sample that is nearly pin hole-free when examined with a light box; FIG. 15C is also nearly pin-hole free after firing at 875° C.

FIGS. 16A, 16B and 16C show Al₂TiO₅, formulation 072716RW3091-1 after a second batch of firing where 16A is a sample pressed in a Carver press at room temperature to form a laminate of 4 layers; 16B shows samples of a large laminate and four single layers of 1.5 in.×0.5 in. samples on a Zirconia substrate for firing and 16C shows samples in the furnace ready for firing at 875° C.

FIG. 17A shows a commercial small-scale tape casting head, 3YSZ films in a bottle, and a glass substrate with casting guide rails.

FIG. 17B shows a wet cast 3YSZ tape.

FIG. 18 shows a wet cast 3YSZ sample 080216RW3091-1 tape.

FIG. 19A-19C show a 3YSZ (080216RW3091-1) where 19A is al 0.5 in.×1.5 in. sample of 3 layers (cracked) and 19B shows sample of 19A folded into quarters and re-pressed. Several 3YSZ single layer samples were then loaded onto a graphite substrate. 19C shows the retort used for N₂ firing containing the repressed sample, five (5) single layer 1.5 in.×1.5 in. samples, two 1 in.×0.5 in., and two 1.5 in.×0.5 in. samples pressed on the lubricious graphite substrate.

FIG. 20A-20C show the conductive graphite plates: (A) showing a freshly polished surface; (B) showing surface changes after firing; and (C) showing samples ready to be fired on top of the lubricious compressible graphite sheet.

FIGS. 21A-21D show an Al₂TiO₅ sample (sample 062016RW3091-1F1500-04) where FIGS. 21A and 21B show the surface at 500× and 2,000× magnification respectively and FIGS. 21C and 21D show the fractured surface revealing internal porosity and a sintered grain structure. There is no apparent delamination.

FIGS. 22A-22D show a fired Al₂TiO₅ sample (Sample 072716RW3091-1-1) where FIGS. 22A and 22B show the surface at 500× and 2,000× magnification respectively and FIGS. 22C and 22D show the fracture surface showing high internal porosity with a well sintered grain structure; there is no apparent delamination.

FIGS. 23A-23D show a fired 3YSZ sample (Sample 080216RW3091-1-10-01) where FIGS. 23A and 23B show the surface at 500× and 2,000× magnification respectively and FIGS. 23C and 23D show the fracture surface showing internal porosity and a sintered grain structure; some minor delamination is shown indicating that the fired 3YSZ can be friable.

FIG. 24 shows an Agilent B1500A display with two probes for measuring resistivity.

FIGS. 25A and 25B show commercially available Celgard® (A) and ManniGlas® (B) separators.

FIGS. 26A and 26B are SEM images taken for Celgard® (A) and ManniGlas® (B).

FIGS. 27A-27D illustrate corrosion testing of three samples of Celgard® separator immersed in 12N HCl (27A), 5M KOH (27B), 5M NaOH (27C) and 2M LiCl (27D) at testing initiation.

FIGS. 28A-28D. illustrate corrosion testing of three samples each of ManniGlas® separator in 12N HCl (28A), 5M KOH (28B), 5M NaOH (28C), and 2M LiCl (28D) at testing initiation.

FIGS. 29A-29D. illustrate corrosion testing of a three samples each of Celgard® separator in 12N HCl (29A), 5M KOH (29B), 5M NaOH (29C), and 2M LiCl (29D) after 26 days.

FIGS. 30A-30D illustrate corrosion testing of a three samples each of ManniGlas® separator in 12N HCl (30A), 5M KOH (30B), 5M NaOH (30C), and 2M LiCl (30D) after 9 days.

FIGS. 31A and 31B show that the Al₂TiO₅ strip is still intact after 12 days (31A) and 68 days (31B) in 12N HCl aqueous solution.

FIGS. 32A-32D show the Celgard® separator after ˜58 days in 12N HCl (32A), 5M KOH(32B), 5M NaOH(32C), and 2M LiCl (32D).

FIGS. 33A-33D. show the ManniGlas® separator after ˜40 days in 12N HCl (33A), 5M KOH (33B), 5M NaOH (33C), and 2M LiCl (33D).

FIGS. 34A-34C show the initial samples of Celgard, ManniGlas, and Al₂TiO₅, respectively, in thionyl chloride.

FIGS. 35A-35C shows samples of Celgard, ManniGlas, and Al₂TiO₅, respectively, in thionyl chloride; the Celgard is transparent in 15 days.

FIGS. 36A-36C show the initial samples of Celgard (A), ManniGlas (B), and Al₂TiO₅ (C) in sulfuryl chloride.

FIGS. 37A-37C shows the samples of Celgard, ManniGlas, and Al₂TiO₅ in sulfuryl chloride after 19 days.

FIG. 38 is a schematic drawing of a glass electrochemical test cell with left and right components.

FIG. 39 is a photograph of the actual glass test cell. Each separator material is evaluated individually by being placed between the two side tubes, the side tubes being held in place with a retainer clamp.

FIG. 40 shows the EC test cell with a Celgard separator being evaluated for ion permeability.

FIG. 41A shows cyclic voltammetry data for Celgard with rising scan rates; FIG. 41B shows the slope extracted from the rising peak.

FIG. 42 shows a custom EC test cell with a ManniGlas separator being evaluated for ion permeability. Because leakage occurred due to the physical properties of the ManniGlass material the cell was wrapped with Parafilm® instead of using a clamp.

FIG. 43A shows cyclic voltammetry data from a potentiostat for ManniGlas with rising scan rates; FIG. 43B shows the slope extracted from the rising anodic peak.

FIG. 44A shows cyclic voltammetry data from a potentiostat for Al₂TiO₅ (sample 072716RW 3091-1-1) with rising scan rates; FIG. 44B shows the slope extracted from the rising peak.

FIG. 45A shows cyclic voltammetry data from a potentiostat for Al₂TiO₅ (Sample 072716RW 3091-1-10) with rising scan rates; FIG. 45B shows the slope extracted from the rising peak.

FIG. 46 demonstrates the flexibility for an Al₂TiO₅ sample.

FIG. 47 is a three dimensional graph showing that curling is minimized by using a large number of layers and a higher pressing temperature.

FIG. 48 is a graph showing that curling is also minimized by using a large number of layers and a lower drying temperature.

FIGS. 49A and 49B show two examples of 1.5 in.×1.5 in. Al₂TiO₅ samples after firing at 1500° C.

DETAILED DESCRIPTION

Described herein is the development of a better performing, cost-competitive, high quality ceramic, rollable separator (CeRollS™) designed to overcome issues associated with other battery separators such as Polytetrafluoroethylene (PTFE) and particularly micro-porous separators used in lithium oxyhalide batteries (LOHBs), specifically batteries requiring frequent field replacement due to safety concerns and increased maintenance costs due to the frequency of necessary maintenance.

The suitability of an all-ceramic separator has been successfully demonstrated, the separator showing flexibility for handling, excellent resistance to typical LOHB electrolytes (thionyl chloride and sulfuryl chloride), and good ion permeability. CeRollS separator samples produced with sizes up to of 1.5 in.×1.5 in. demonstrated apparent porosities ranging from 6.5-49.9%, for fired thicknesses of ˜102-195 μm. Sample pore diameters varied, based on thickness and processing parameters, from 0.50-42 μm. While other commercial separators such as ManniGlas 1200 (fiberglass) decomposed in 12N hydrochloric acid (HCl) in 9 days and white Celgard (polyethylene-propylene) turned transparent in thionyl chloride after 15 days, CeRollS separators described herein were still intact to the extent of testing, i.e., after >89 days in 12N HCl, >54 days in thionyl chloride, and >19 days in sulfuryl chloride.

Processing conditions changes have been identified to improve the tape casting formulation, drying, and firing processes to:

-   -   1. Increase flexibility, handleability, and safety for an         all-ceramic separator,     -   2. Produce larger, full-size separators at-least three (3)         inches across,     -   3. Increase production capabilities to provide sufficient         improved samples to be used for further testing of ion         permeability, chemical stability and electrical resistivity, and     -   4. Provide cell level testing including tensile strength with a         target of <2% offset at 1,000 psig and a puncture strength >300         g/mil.

A key motivation for the CeRollS development work was to develop a new LOHB separator with improved performance and an increased operational lifetime resulting in decreased operating costs. The target product is illustrated in FIGS. 1A-1C. FIG. 1A illustrates an assembled battery 100 containing a rolled structure 102, said rolled structure 102 shown in a cut-away view in FIGS. 1B and 1 n a further enlarged view in FIG. 1C. The ceramic separators 104 separate the positive electrode 106 and negative electrodes 108 assembled in a rolled structure 110 (FIG. 1A) with the positive electrodes 106 (FIG. 1C) connected to a positive electrode collector 112 and the negative electrodes 108 connected to a negative electrode collector 114. While the Figures illustrate a rolled structure, the ceramic separators 104 and can easily be used in planar stacked Li batteries.

As alternate ceramic separators, a flexible 3 mol % Yttria Stabilized Zirconia (3YSZ) material and aluminum titanate (Al₂TiO₅) (Rivero, Palacio F. “Reactive Sintering of Aluminum Titanate”; Irene Barrios deArenas; Instituto Universitario de Tecnologia; Venezuela; p. 503. http://cdn.intechopen.com/pdfs/29796.pdf), said article incorporated herein in its entirety by reference, were evaluated. These potentially flexible materials were produced by two different mechanisms: (a) strain relief theory for YSZ and (b) microcrack hinge theory for Al₂TiO₅. Tape casting was used to successfully produce thin flexible green films which were then fired to form thin films for use as battery separator membranes, a use not shown nor suggested in the literature. CeRollS separators: (a) electrically isolate electrodes, (b) have suitable ion permeable, (c) withstand corrosive electrolytes, (d) are suitable for a production environment, including demonstrate mechanical flexibility and handling, (e) maximize volumetric efficiency for electrolyte capacity, (f) have an extended shelf life, and (g) provide optimized efficient electrolyte flow and distribution.

The overall goal was to develop a new LOHB separator with improved performance, lower cost and increased operational lifetime, based on a cast and fired all ceramic, flexible tape material. The CeRollS product was also evaluated for corrosion resistance over time and ion permeability. While the material was not as flexible as intended, all the other objectives were met. Initial examples of fired Al₂TiO₅ measured 1.5 in.×1.5 in. Two examples (identified as samples 072716RW3091-1-5 and 072716RW3091-1-10), shown in FIGS. 2A and 2B were fired in different lots, using the same firing conditions. Apparent porosities ranged from 6.5 to 49.9% for samples with fired thicknesses of ˜132-195 μm. A variety of parameters including tape casting slip formulation, tape cast head gap, drying techniques, low temperature (120° F.) press lamination, and furnace firing profiles were evaluated to develop an initial, partially optimized process. Superior resistance to corrosion from thionyl chloride was achieved. The details of corrosion testing and resistance to other electrolytes tested (12 N HCl and sulfuryl chloride) are discussed below. Volume electrical resistivity was also measured and is described below. The resistivities were >3.43×10¹¹ for Celgard, >1.60×10⁹ for ManniGlas, and >5.43×10⁸ Ohm-cm for Al₂TiO₅. While the Al₂TiO₅ sample measured at ˜10⁹ Ohm-cm, the measured value is acceptable, when compared to the text book value for Al₂TiO₅ of 10¹⁴ Ohm-cm, the lower measured value is possibly due to the limitations of the Agilent test unit, or to impurities from processing. Electrometer measurements are being pursued to clarify this discrepancy.

Table 1 summarizes the target properties and the properties of the materials actual produced.

TABLE 1 COMPARISON OF CeRollS FORMULATIONS TO TARGET LITHIUM BATTERY SEPARATOR PROPERTIES PARAMETER TARGET Using Al₂TiO₅ USING 3YSZ MATERIAL 100%_(w) Ceramic 100%_(w) Ceramic 100%_(w) Ceramic THICKNESS 25 μm Fired 160-368 μm dry; 110-163 μm dry; fired ≈ 132-195 μm fired 102-59 μm PORE SIZE <1 μm: preferred 3-42 μm 0.5-6 μm <200 nm POROSITY ≈40% 6.5-40.8% MELT INTEGRITY 150° C. ≤1500° C. ≥875° C. CORROSION Better Than Intact >89 days in RESISTANCE Commercial 12N HCl. Electrolytes Intact >54 days in & >1 wk without thionyl chloride. degradation in Intact >19 days in common sulfuryl chloride electrolytes CHEMICAL STABILITY 10-year Need accelerated Need accelerated shelf life battery life testing- battery life phase II testing-phase II THERMAL OPERATING −40 to +120° F. −40 to >>120° F. −40 to >>120° F. RANGE THERMAL STABILITY <5% shrinkage (Calculated) (Calculated)

a Al₂TiO₅ −0.05%;

 3YSZ 0.18%;

b Al₂TiO₅ −0.19%;

c Al₂TiO₅ −0.35% VOLUME RESISTIVITY Al₂TiO₅ Al₂TiO₅ > 5.4 × 10² (Ohm-cm) ION PERMEABILITY Better than Better than TYPICAL Conventional Conventional ELECTROLYTES Celgard or Celgard or ManniGlas ManniGlas in a ferric-ferrous redox couple in aqueous electrolyte RESISTANT TO Resistant to Resistant to immersion Resistant to CORROSION BY immersion in in thionyl chloride immersion in OXYHALIDE thionyl chloride and sulfuryl chloride thionyl chloride ELECTROLYTES and sulfuryl and sulfuryl chloride chloride COST EFFICIENCY Dependent on Dependent on Dependent on economy of scale economy of scale economy of scale FLEXIBILITY Able to wrap Some flexibility around 8 mm (≈25° on a bend mandrel without test; to be improved breaking in Phase II DECREASED Dependent on Dependent on Dependent on MANUFACTURING economy of scale economy of scale economy of scale COMPLEXITY-

CeRollS also exhibited good ion permeability when compared with the performance of commercial separators. Celgard showed 2.56×10^(−19 cm2)/sec while ManniGlas showed ˜7.50×10⁻¹⁶, Al₂TiO₅ (Sample 1) exhibited ˜1.16×10⁻¹⁵, and Al₂TiO₅ (Sample 2) exhibited ˜1.75×10⁻¹⁵ cm²/sec. Sample 1 showed the best (most desirable) ion permeability.

Efforts also focused on developing a ceramic slip from both 3YSZ and Al₂TiO₅, casting the slip, successfully firing samples, and performing initial tests. To this end, applicant successfully developed slip formulations for tape casting nanoparticle Al₂TiO₅ and 3YSZ, designed and developed an all-ceramic separator material, fabricated 1.5 in.×1.5 in. samples, and successfully tested the ion permeability, corrosion resistance and resistivity of CeRollS.

Suitable conditions for low temperature press lamination for thicker and intrinsically pin hole free tapes were established. In addition, it was found that some improvements in strength can be obtained with longer firing times and higher firing temperature. Testing showed favorable high resistivity, good ion permeability, and good corrosion resistance. Based thereon this data indicates that a robust, flexible, all-ceramic LOHB battery separator that can be used in a broad range of battery applications can be produced.

Materials

Yttria Stabilized Zirconia (YSZ) and aluminum titanate powders, the raw materials for ceramic membrane separators, were obtained from two suppliers. Thionyl chloride and sulfuryl chloride (electrolytes for LOHBs) were used in corrosion testing of the ceramic membrane separators. Additional corrosive liquids, such as HCl and potassium hydroxide were used to fully characterize the ceramic membranes. Supplies such as mirror finish pressing platens, firing substrates to process the membrane separators were also used. Platinum working electrodes and custom glass test cells were used for ion permeability testing. Two commercially available separator materials (Celgard® and ManniGlas®) were used for comparative performance standards.

Fabricating Flexible, Fully Ceramic Separators

Films were prepared from commercially available Al₂TiO₅ (two different sources) or 3YSZ following characterization using scanning electron microscopy (SEM, Photometrics, Huntington Beach, Calif.). The first source (Sigma Aldrich (SA)) had jagged particle size of ˜15-30 μm (See FIGS. 5A and 5B). A second source of the Al₂TiO₅ powder (American Elements (AE)) is reported to be <325 mesh and 99% pure (metals basis) with a particle size at <44 μm. These two sources of Al₂TiO₅ sources allowed evaluation of two different particles sizes for forming the tapes. FIGS. 6A and 6B show Al₂TiO₅ from AE to have a jagged particle size at ˜5-20 μm. FIGS. 7A and 7B show the 3YSZ powder to have large agglomerates of 1-10 μm, with an ultimate particle size of ˜40 nm. Making films from nanopowder is often more challenging than making films from powders in the 1-10 μm particle size range.

FIGS. 8A and 8B show X-Ray Diffraction of the two different Al₂TiO₅ starting powders. Al₂TiO₅ is known to have an orthorhombic structure and is isomorphous with a pseudobrookite structure similar to (Fe₂TiO₅). The d-spacings are a function of impurities, and also may be modified by stresses that build up in Al₂TiO₅ due to processing and the intrinsic structure of the phase. The Al₂TiO₅ has average d-spacings of 4.70, 3.35, 2.65, and 1.90). (Ogunwumi, S B and Tepesch, P D; “Ceramic Body Based On Aluminum Titanate and Including a Glass Phase”; United States; Patent Application Publication; US 2006/0064957 Pub. Date: Mar. 30, 2006).

The black color of the AE Al₂TiO₅ sample and the white color of the SA Al₂TiO₅ are in stark contrast. However, after firing the color of the AE sample became an off white. The effect is presumed to be caused by lattice oxygen deficiency. On firing in air, the lattice takes on more oxygen to produce the lighter off-white color. However, both are Al₂TiO_((5-x)), where x is variable based on synthesis method and firing profile of the final material.

An X-Ray diffraction pattern shown in FIG. 9A was also generated for the 3YSZ. The major peaks are in close agreement with the spectrum shown in the literature. (FIG. 9B; Patil D S; Prabhakaran K; Durgaprasad C; Sharma, S C; “Synthesis Of Nanocrystalline 8 Mol % Yttria Stabilized Zirconia By The Oleate Complex Route; Ceramics International, January 2009, 35 (1); p 515-519) Fabricating Ceramic Separators—Al ₂TiO₅

Disks and tape were both cast from Al₂TiO₅. The technical literature discusses the flexibility property of fired, pressed pellets of ceramic Al₂TiO₅. Described herein are the formation of disks of Al₂TiO₅ to evaluate flexibility. Evaluated were the optimum firing cycle and limits on thickness to be applied in casting tape samples. The resultant properties were compared to data in the literature. (Halford G. R.; “Fatigue and Durability of Structural Materials of Structural Materials”; ASM International, 2006, p 405). Al₂TiO₅ formulations were adjusted to achieve easy casting into tape, good crack-free drying, and crack-free firing.

Initial disk samples were formed using the Al₂TiO₅ powder without any added vehicle. However, after pressing the edges of the disk fell away. Therefore, a formulation was then made using several alternative fugitive organic vehicles/binders (Edge-Tech Industries LLC. YSZ (Yttria Stabilized Zirconia). URL:http://www.edgetechind.com/Products/Refractory-Metals/Zirconium/Chemicals/YSZ-Yttria-Stabilized-Zirconia-719-1.html). Fractured cross sections of the Al₂TiO₅ disks were examined using SEM (Photometrics). The grain morphology was the same in both the literature and samples prepared (FIGS. 10A-10D). However, the grain size of the samples prepared had a grain size 4× that shown in the literature. Also, while disks produced were not pressed at high pressures and a good binder had not yet been identified, the binder used in tape casting was found to be more effective and tape pressing was then accomplished using higher pressures and temperatures to provide suitable lamination in the cast tape samples.

Tape Casting of Al₂TiO₅—

The initial pressed sample sizes were kept small, to allow evaluation of numerous different formulations while consuming as little material as possible in order to identify a material composition having acceptable flow characteristic. FIG. 11A-11C show, respectively, the ball mill, the powdered sample in the ball jar, and the sample produced. The initial formulation appeared to have good flow characteristics for tape casting. The material was de-aired prior to casting. While cosmetic flaws, such as thin areas were present, fired dried tape was formed to obtain initial information on thickness and fired flexibility.

FIGS. 13A and 13B show an improved composite Al₂TiO₅ tape resting on a light box. FIG. 13A shows the dried Al₂TiO₅ tape (Sample 062016RW3091-2) in ambient light. FIG. 13B shows the use of the light box for inspecting the dried tape for pinholes. The tape was smooth and without any large pinholes. However, about a dozen small pinholes («1 mm) were visible using a magnifying glass.

Several samples of the Al₂TiO₅ tape were prepared, including a single unpressed tape, a pressed two-layer tape and a pressed three-layer tape sample. Pressing was performed at a nominal 3 Klb at 52±1° C. (125±2° F.). The nominal initial size was ½ in.×1 in. in all three cases, with thicknesses from 0.18 to 0.40 mm (See Table 2).

TABLE 2 Tape Thickness 1 Layer 2 Layer 3 Layer (mm) (unpressed) (pressed) (pressed) Average 0.18 0.28 0.40 Standard deviation 0.01 0.03 0.02

The samples were then fired at 1500° C. The unfired samples are shown on an alumina substrate in FIG. 14A; the fired samples are shown on the same alumina substrate in FIG. 14B. The black color of the initial Al₂TiO₅ is due to a stoichiometric deficiency of oxygen. After firing in air, the dark color is substantially eliminated, as evidenced by a lighter coloration for the fired samples. The fired product was continuous and did not degrade to a powder on firing at 1500° C. for 8 hours. Further, they were easily removed from the substrate as there was no adhesion to the substrate after firing. The fired tapes did not, however, exhibit as much flexibility as desired (wrapping 270° around an 8 mm mandrel). The fired tape thicknesses were subsequently measured using a caliper micrometer. Subsequent samples prepared at higher temperatures and longer firing times appeared to improve flexibility of the end product.

Al₂TiO₅ (Sample 072716RW3091-1)—

These samples were prepared using the Al₂TiO₅ powder obtained from SA. Initially, some separation of the powder from the binder was observed when the material was allowed to sit for several days before firing. However, the material was usable following processing on a roll mill, which is a technique that is used in some tape casting monolithic capacitor production facilities. When scaled up to four times the size of the original, the formulation appears to have good flow characteristics for tape casting.

The Al₂TiO₅ material was cast to a thin dried layer 230 μm (0.23 mm) thick. Four (4) fired samples, one of which is shown in FIG. 15, as well as an additional five (5) samples (FIG. 16) were produced. The Al₂TiO₅ tape samples were fired with a 16 h cool down which provided time for improved structural development and flexibility, the result being one acceptable tape and one badly curled tape.

Al₂TiO₅ (Sample 080916RW3091-1):—

These samples were prepared using the Al₂TiO₅ powder obtained from AE. The sample sizes were again deliberately kept small until suitable flow characteristics were established. This formulation was cast easily and had the desired viscoelastic properties typical of a good casting material. A larger batch was later used for casting tapes.

Fabricate Ceramic Separators—3YSZ

Several tape samples were cast from nanopowder 3YSZ. FIG. 17A shows a manual commercial tape casting head used to prepare the tapes, the 3YSZ slip in a de-airing jar, and a sample of a cast tape on a glass substrate.

3YSZ (Sample 080216RW3091-1)—

Tapes of 3YSZ were successfully cast from a formulation comprising the powdered 3YSZ material. The film was then placed on a graphite substrate and fired in a nitrogen atmosphere. The 3YSZ material had a high viscosity but was stable and showed no separation of constituents after de-airing and standing following de-airing. It was cast successfully to form a 3YSZ tape. Samples were then cut from the tape and fired both as single and pressed multiple layers for various different time periods. The tape, shown in FIG. 18, shows some irregularities but no thin or open areas were seen for previously.

Additional samples were cut from the same 3YSZ tape (Sample 080216RW3091-1). A 1.5 in.×1.5 in. sample was laminated to produce a 3 layer. The tape cracked in the center of the piece in the green state (prior to firing) so the piece was turned and folded into quarters, and re-pressed (FIG. 19). To produce additional usable samples, additional 3YSZ single layer pieces were loaded onto a pressed, lubricious, hard graphite substrate including one 1.5 in.×1.5 in. piece, two 1 in.×0.5 in. pieces and two 1.5 in.×0.5 in. pieces. (FIGS. 19B and 19C).

Graphite Substrates

The lubricious graphite substrate provides a better surface which eliminates adhesion of the sample onto the surface during firing. The lubricious graphite also appears to provide a better substrate for preventing curling during the drying process. Thicker (0.25 in.) load plaques were also fired, but resulted in complete cracking of all the parts. All the samples showed some degree of curling after firing.

The 3YSZ samples were fired on top of a smooth graphite surface. In order to prevent the graphite from oxidizing, the samples were fired in a retort with flowing nitrogen. The polished graphite substrate surface is shown in FIG. 20A. During the firing, the high temperature, conductive, premium sheet, ¼″ thick, 6″×6″ graphite surface under each sample became modified (FIG. 20B), so the surface was repolished before each use (FIG. 20C). By repolishing after each use, these ¼ inch thick graphite substrates can be used for many subsequent firings.

As an alternative, the use of a thinner ( 1/16-inch thick) lubricious compressible graphite sheet was considered. However, while the thinner sheet was found to be more difficult to clean, it did not tend to acquire a rough surface after each firing.

Comparison of Al₂TiO₅ and 3YSZ Tapes and Fired Parts

The thickness of a cast tape after drying was found to be a function of the casting formulation, the gap on the casting device, room temperature and relative humidity during casting, and casting speed. However, while the thickness of the dried, cast film is relevant to the final fired thickness, other parameters are also relevant in determining fired thickness. All tapes were cast using a manual casting production head. However, an automated casting machines will perform the same process with greater uniformity than manual casting. To demonstrate the range of dried cast thicknesses that could be achieved, the thickness was measured using a caliper micrometer. Table 3 shows that the thickness measured for various dried tapes ranging from 0.11 to 0.37 mm

TABLE 3 RANGE OF THICKNESSES (MM) ACHIEVABLE FOR UNFIRED CAST DRIED FOR MDA TAPE SEPARATOR PRECURSOR MATERIAL Al₂TiO₅ Al₂TiO₅ Vendor 1 Al₂TiO₅ Al₂TiO₅ 3YSZ 3YSZ Vendor 1 Scaleup Vendor 2 Vendor 2 Vendor 1 Vendor 1 062016R 072716R 080916R 080916R 062016R 080216R W3091-2 W3091-1 W3091-1 W3091-1 W3091-1 W3091-1 Unfired Unfired Unfired Unfired Unfired Unfired 8-20-16 9-8-16 0.150 0.290 0.340 0.380 0.178 0.140 0.160 0.310 0.330 0.330 0.178 0.130 0.150 0.180 0.390 0.300 0.102 0.090 0.170 0.190 0.390 0.380 0.203 0.090 0.170 0.200 0.390 0.310 0.152 0.100 STANDARD DEVIATION 0.010 0.061 0.030 0.038 0.038 0.023

Fired Tape Thicknesses—Apparent Densities

The thickness, width, and length of each unfired sample was measured three times and the thickness, width and length of each fired tape was measured five (5) times using a caliper micrometer. The samples were also weighed and the data was used to determine apparent density. Using

ρ_(app)=(ρAl₂TiO₅−ρ Sample)/ρAl₂TiO₅

the apparent porosity (ρapp) of the Al₂TiO₅ tape was then calculated, assuming that the density of pure Al₂TiO₅ is 3.35 g/cm³. The theoretical density of bulk Al₂TiO₅ was used to calculate the apparent densities of the tapes. Note the average thickness (thAV) in Table 4 is the average of three thickness readings for samples. As shown in Table 4, the apparent porosity for the first firing was ˜40-50% while the second firing resulted in apparent densities of ˜33-36%. Subsequent firings provided apparent densities of ˜12-40%. While the reasons for the range of values is unclear, curling of many substrates made it difficult to obtain consistent values. Fired Tape—Microstructure: Al₂TiO₅

Al₂TiO₅ (Sample 062016RW3091-1) tapes were successfully produced and, with practice, could be handled. Tapes were cut, in some instances laminated at pressure and low temperature, and then firing at 1500° C.

FIGS. 21A-D show SEM images of representative samples of fired Al₂TiO₅. As shown in FIGS. 21A and 21B the surfaces of the tapes appear to be well sintered. In cross section (FIGS. 21C and 21D), they also appear well sintered, with no microscopic delamination but exhibit microcracking characteristic of flexible Al₂TiO₅. This microcracking seen the upper FIGS. 21A and 21B compares well with examples from the literature. (Babalot C.; Guignard A.; Huger M.; Gault C.; Chotard T.; Ota, T.; Adachi, N.; “Preparation and Thermochemical Characterization Of Aluminum Titanate Flexible Ceramics”. Journal of Material Science, 2011. 46, p 1211-1219).

TABLE 4 DENSITIES OF FIRED AL₂TIO₅ TAPE SAMPLES Den- sity Poros- Material SAMPLE Layers Size thAV g/cm³ ity Al₂TiO₅ 070516RW3091-2 1 0.5 × 1.5 0.023 1.696 0.494 Al₂TiO₅ 070516RW3091-2 2 0.5 × 1.5 0.026 2.126 0.365 Al₂TiO₅ 070516RW3091-2 3 0.5 × 1.5 0.041 1.980 0.409 Al₂TiO₅ 071516RW3091-1 1 0.5 × 1.5 0.014 2.639 0.212 Al₂TiO₅ 071516RW3091-1 2 0.5 × 1.5 0.019 2.814 0.160 Al₂TiO₅ 071516RW3091-1 3 0.5 × 1.5 0.024 3.131 0.065 Al₂TiO₅ 062016RW3091-2-1 1 0.5 × 1.5 0.012 3.133 0.065 Al₂TiO₅ 062016RW3091-2-8 1 0.5 × 1.5 0.016 2.384 0.288 Al₂TiO₅ 062016RW3091-2-9 1 0.5 × 1.5 0.015 2.454 0.268 Al₂TiO₅ 062016RW3091-2-10 1 0.5 × 1.5 0.013 2.960 0.116 Al₂TiO₅ 062016RW3091-2-11 1 0.5 × 1.5 0.016 2.206 0.341 Al₂TiO₅ 062016RW3091-2-12 1 0.5 × 1.5 0.014 2.622 0.217 Al₂TiO₅ 062016RW3091-2-13 1 0.5 × 1.5 0.019 1.982 0.408 Al₂TiO₅ 062016RW3091-2-14 1 0.5 × 1.5 0.013 2.747 0.180 Al₂TiO₅ 062016RW3091-2-15 1 0.5 × 1.5 0.013 2.742 0.182 Al₂TiO₅ 062016RW3091-2-16 1 0.5 × 1.5 0.013 2.871 0.143

Al₂TiO₅ (Sample 072716RW3091-1-1) tapes were also successfully produced. Tapes were cut, and in some cases laminated under pressure and low temperature, and then fired at 1500° C. They also could be manipulated if handled carefully. FIGS. 22A-22D show SEM images of representative samples of fired Al₂TiO₅. On the surface (FIGS. 22A and 22B), and in cross section (FIGS. 22C and 22D) also appear well sintered with no microscopic delamination, but high porosity and microcracking characteristic of flexible Al₂TiO₅ was observed.

Fired Tape—Microstructure: 3YSZ

3YSZ tapes were also fabricated successfully but were relatively thin. Tapes were cut, and in some cases laminated at pressure and low temperature, followed by firing at 850-875° C. However, they were friable and difficult to handle. FIGS. 23A-23D show SEM images of selective, representative fired samples of 3YSZ tapes. On the surface (FIGS. 23A and 23B), appear well sintered. However, in cross sections (FIGS. 23C and 23D), they show microscopic delamination which was not evident macroscopically. The friability can be attributed, at least in part, to the minor delamination. Fired thicknesses were initially measured using a handheld caliper micrometer. However, it was found that more accurate measurements could be determined by SEM fracture cross sections.

The cross sections (FIGS. 21A-21D, 22A-22D and 23A-23D) were used to determine the fired thickness and the pore size. These are summarized in Table 5. The fired thicknesses for these various samples are comparable. Thickness can be increased by laminating multiple layers. Caliper micrometer measurements include some camber, and are therefore greater in value to a maximum of about 380 μm. Pore size varies as a function of formulation, laminating time and temperature, and firing temperature profiles. Further modification of the pore size can be obtained by use of suitable porogens.

TABLE 5 FIRED AL₂TIO₅ AND 3YSZ TAPE SAMPLE CHARACTERISTICS FROM SEM Thickness Pore Size Material Sample ID (μm) (μm) Al₂TiO₅ 062016RW3091-1- 132 3-9 F1500 Al₂TiO₅ 072716RW3091-1 195  6-42 3YSZ 080216RW3091-1-10 ~102-159 0.5-6   Evaluating Thermal Expansion, Resistance to Corrosion from LOHB Electrolytes, Electrical Insulation, and Ion Permeability of CeRollS

Thermal Expansion

The thermal expansion coefficients for the two candidate materials are as follows:

-   -   3YSZ α=11×10⁻⁶/° C.         -   (EdgeTech Industries LLC. YSZ (Yttria Stabilized Zirconia).         -   URL:http://www.edgetechind.com/Products/Refractory-Metals/Zirconium/Chemicals/YSZ-Yttria-Stabilized-Zirconia--719-1.html)     -   Al₂TiO₅     -   For Al₂TiO₅, with an orthorhombic crystal structure, the         relationship is:

β_(v)=α_(a)+α_(b)+α_(c)

-   -   -   Where β_(v)=Volumetric thermal expansion coefficient             -   α_(i)=thermal expansion coefficients of principal                 crystal axes

α_(a)20−520−α_(a)20−1000=−2.9−−3×10⁻⁶/° C.

α_(b)20−520−α_(b)20−1000=10.3−11.8×10⁻⁶/° C.

α_(c)20-520−α_(c)20−1000=20.1−21.8×10⁻⁶/° C.

-   -   (Rivero Palacio F. “Reactive Sintering of Aluminum Titanate”;         Irene Barrios de Arenas; Instituto Universitario de Tecnologia;         Venezuela; p. 503. http://cdn.intechopen.com/pdfs/29796.pdf)

The temperature range of interest is −40° C. to >120° C. (−40° F. to >>248° F.). Therefore, using the largest of the values, the thermal expansion over the temperature range of interest is as follows:

For α_(3YSZ)(−40° C.−1000° C.)=11×10⁻⁶×(160)=0.18%

For α_(a Al2TiO5)(−40° C.−1000° C.)=−3×10⁻⁶×(160)=−0.05%

For α_(b Al2TiO5)(−40° C.−1000° C.)=11.8×10⁻⁶×(160)=0.19%

For α_(c Al2TiO5)(−40° C.−1000° C.)=21.8×10⁻⁶×(160)=0.35%

Using these formulas, the thermal expansion was calculated to be well below the <5% expansion desired for the separator over the temperature range of interest. Electrical Insulation (Electrical volume resistivity)

Typical definitions of material resistivities are:

for conductors (≤10⁻⁸ Ω·cm),

for semiconductors (˜10⁻⁸-10¹⁶ Ω·cm), and

for insulators (≥10¹⁶ Ω·cm)·7

The formula for calculating resistivity is:

ρ=R·A/

where:

-   -   R is the electrical resistance of a uniform specimen of the         material (measured in ohms),     -   A is the cross-sectional area of the specimen (measured in         square meters) and     -   is the length of the piece of material (measured in meters).

High impedance resistivity measurements were made using an Agilent B1500A Semiconductor Device Analyzer Mainframe with B1500A-903 Power Cord and B1511AFG Medium Power Source/Monitor Unit Module (Agilent Technologies, Inc.; Wilmington, Del.) together with a set of 5 pound RT-1000 and CP-1111 Concentric Ring Probe electrodes (Static Solutions, Inc., Marlborough, Mass.), shown in FIG. 24. Celgard, ManniGlas, and Al₂TiO₅ samples were measured. There was substantial noise in the data, indicating the samples were near or within the detection limit, so the values found are minimum resistance values. The data for volume resistivity is shown in Table 6. Since the text book value for Al₂TiO₅ is 10¹⁴ Ohm-cm, the lower measured value may be due to the limitations of the Agilent test unit, or to impurities from processing.

TABLE 6 RESISTIVITY MEASUREMENTS Celgard ManniGlas Al₂TiO₅ Amperage  <1.78 × 10⁻⁹  <2.52 × 10⁻⁸  <7.37 × 10⁻⁷ (amps) Resistance  >1.69 × 10⁸  >1.2 × 10⁸  >4.07 × 10⁶ Voltage (volts)    3    3    3 Diameter (inch)    1    1    1 Sample   25 μm   381 μm   380 μm thickness Resistivity  >3.43 × 10¹¹  >1.60 × 10⁹  >5.43 × 10⁸ (Ohm-cm) Resistance to Corrosion from LOHB Electrolytes

Commercial Separators:

As set forth above, two commercial separator materials, Celgard® and ManniGlas®, were used as reference standards for testing. SEM images of the surface of the Celgard and ManniGlas separators materials are shown in FIGS. 25A and 25B respectively. The Celgard pore size ranges from about 60 to about 120 nm. It should be noted that Celgard is very easily stretched, so much larger values can be obtained by stretching the material. The pore size for the ManniGlas is listed in the literature as much larger, but the value is unclear as a cross section of the ManniGlas appears to show a much smaller effective pore size.

Corrosion testing was conducted on control samples of the separators. Twelve samples of 1 in.×1 in. squares of Celgard separator was weighed and then placed in individual glass vials with 15 mL of electrolyte. Three samples were tested in each of the following electrolytes.

-   -   Hydrochloric acid—commercial 12N HCl aqueous solution     -   Potassium hydroxide—5 molar aqueous solution     -   Sodium hydroxide—5 molar aqueous solution     -   Lithium chloride—2 molar aqueous solution     -   Sulfuryl chloride     -   Thionyl chloride

FIGS. 27A-27D shows 12 vials containing Celgard samples at the start of testing and FIGS. 28A-28D show 12 vials of ManniGlas samples at the start of the corrosion tests. The samples were viewed and photographed once a week.

FIGS. 29A-29D show images of the Celgard containing vials after 26 days of exposure to the electrolytes. FIGS. 30A-30D show the ManniGlas samples after 9 days exposure. The flexible ceramic substrates produced as described herein were subjected to the same exposure testing

The ManniGlass samples in 12N HCl was destroyed by the HCl, no discernible separator material remained and only a cloud of loose glass fibers was observed. On the other hand, a fired sample of Al₂TiO₅ tape exposed to 15 mL of a 12N HCl aqueous solution was intact after 12 days, (FIG. 31A) and after 68 days (FIG. 31B).

FIGS. 32A-32D show vials containing Celgard after exposure for 58 days and FIG. 33A-33D show ManniGlas after exposure for 40 days in the KOH, NaOH and LiCl.

Corrosion Testing in Thionyl Chloride

Celgard, ManniGlas, and Al₂TiO₅ samples were also placed in 99% thionyl chloride. FIGS. 34A-34C show images of the initial immersion. The Celgard in thionyl chloride was transparent after 15 days (FIG. 35A) while the CeRollS Al₂TiO₅ appears to be unchanged (FIG. 35C).

Corrosion Testing in Sulfuryl Chloride

Celgard, ManniGlas, and Al₂TiO₅ samples were also tested in 97% sulfuryl chloride. Samples of Celgard, ManniGlas, and Al₂TiO₅ immersed in sulfuryl chloride. are shown in FIG. 36A-36C respectively. No degradation of the separator materials was seen on the initial day of immersion. FIGS. 37A-37C show samples of Celgard, ManniGlas, and Al₂TiO₅ immersed in sulfuryl chloride after 19 days immersion; no degradation of the separator materials was observed. The Celgard, ManniGlas and the Al₂TiO₅ samples still appear to be unaffected >26 days in thionyl chloride. The corrosion results for the various materials are summarized in Table 7 below.

TABLE 7 SUMMARY OF CORROSION RESISTANCE Property/ Celgard ® Manniglas ® ISL Al₂TiO₅ Material (2325) 1200 CeRollS CHEMICAL PROPERTIES Material 100 wt % Fiberglass-polymer 100 wt % polyethylene- composite ceramic polypropylene PP/PE/PP Corrosion Transparent in Decomposed Intact at 89 days resistance thionyl chloride in 12 N HCl in in 12N HCl, in 15 days, 9 days, Intact at Intact at 54 days Intact at 86 days 54 days in in thionyl chloride, in 12N HCl, thionyl chloride, & Intact at 19 days Intact at 26 days Intact at 26 days in sulfuryl chloride in sulfuryl in sulfuryl chloride chloride

Ion Permeability

The test apparatus 120 for testing ion permeability consists of two matching glass receptacles (test cells) 122 with side arms 124 which provide an interconnecting region extending from the side of each test cell. Flat separator samples 126 were placed between the side arms 124 and these two side arms 124 were joined with a clamp 128 or sealing wax 130. An electrolyte 132 was poured into each of the glass receptacles 122. The open tops 134 of the receptacles 122 each had Teflon plugs 136 with platinum electrodes 138 penetrate therethrough and into the test electrolyte 132 in the receptacles 122. A schematic drawing of the test apparatus is shown in FIG. 38. FIGS. 39 and 40 show the glass test cells 122 assembled together with the separator samples 126 extending across the junction of the cells. The two commercial grade separator materials (Celgard 25 μm batch 0011603 and 0.015 inch thick ManniGlas 1200) were evaluated using this two chambered electrochemical (EC) cell 120. Their cyclic voltammetry profiles were measured in aqueous salt solution using a Princeton Applied Research Potentiostat Model 265A.

A 1.5-inch square of separator material 126 was placed between the side arms 124 of the two receptacles 122 of the EC cell 120 and secured using O-Rings 1 (not shown) and a clamp 138 (FIG. 40). The cell was then filled with the electrolyte solution 132 composed of 0.1 M sodium sulfate and 0.01 M potassium ferrocyanide. A total of 40 mL of the electrolyte solution was used to fill the cells with. 20 mL on either side of the separator 126 (in each chamber). A pair of platinum electrodes 138 with active areas of 0.31 cm² was used, with an electrode 138 placed in each receptacle 122 half cell on either side of the separator 126. After the electrical connections were made, cyclic voltammetric sweeps were conducted between −1 to +1 V. The cyclic voltammetry data for the Celgard sample is shown in FIGS. 41A and 41B.

The diffusion coefficient of the separator was calculated using the slope extracted from the anodic peak current versus square root of the scan rate plot shown in FIG. 41B based on the rearranged Nernst equation below:

$D = \left( \frac{Slope}{2.69 \times 10^{5} \times n^{3/2} \times A \times C_{o}} \right)^{2}$

Where:

D is the diffusion coefficient

n is the electron transferred

A is the surface area of the working electrode, and

C_(O) is the molar concentration

Using the Nernst equation, the diffusion coefficient was calculated to be 2.562×10⁻¹⁹ cm2/s for Celgard.

The same experiment was repeated for the ManniGlas 1200 separator (Lydal Performance Materials, Inc., NY). However; after setup, the sponge-like properties of wetted ManniGlas caused the electrolyte to seep out of the cell despite the pressure applied by the O-Rings (FIG. 42). In order to prevent leakage, Parafilm® (Bemis N A, Wis.) 130 was used to further seal the joint and prevent the electrolyte from seeping out of the cell. The cyclic voltammetry was then conducted and the data shown in FIGS. 43A and 43B was generated. Utilizing the Nernst equation above, the diffusion coefficient was calculated to be 7.50×10⁻¹⁶ cm²/s.

The same experiment was repeated for two ISL CeRollS Al₂TiO₅ separators. Cyclic voltammetry was conducted and the data generated for these two samples is shown in FIGS. 44A, 44B, 45A and 45B. Using the Nernst equation, the diffusion coefficient was calculated to be, 1.162×10⁻¹⁵ and 1.75×10⁻¹⁵ cm2/s, respectively.

In summary, ManniGlas® has a higher rate of diffusion than Celgard®. However, Celgard is more robust and does not deteriorate in 12N HCl. The electrochemical evaluation of ISL's CeRollS separator material compared with commercial separator materials is summarized in Table 8. Al₂TiO₅ has the lowest (most desirable) ion permeability at ˜10⁻¹⁵ cm²/sec.

TABLE 8 THE ION PERMEABILITY VALUES FOR TWO COMMERCIALLY AVAILABLE CONTROLSEPARATORS AND TWO CEROLLS BASED ON AL₂TIO₅ PARA- METER CELGARD ® MANNIGLAS ® Al₂TiO₅ Al₂TiO₅ D 2.56 × 10⁻¹⁹ 7.50 × 10⁻¹⁶ 1.16 × 10⁻¹⁶ 1.75 × 10⁻¹⁶ (cm²/s) THICK- 25 381 132 185 NESS, μm

Mechanical Flexibility

Normally failure in ceramic materials has been catastrophic, meaning that a crack usually propagates resulting in a catastrophic failure of the piece. However, there are a variety of exceptions to this rule. A salt crystal can bend nearly 360 degrees in water, since the dislocations are dissolved in the bending process. In recent years, high temperature super-plasticity has been widely reported for some ceramic systems. Two different mechanisms of failure for the presently described ceramic materials were evaluated. Flexibility was quantitatively measured using a test device 154, shown in FIG. 46, consisting of a small photographic copy stand 140, a standard digital camera (not shown), a standard third arm tool 142, a protractor 144, a stationary wooden vertical member 146 resting on the copy stand base, and a parallel movable wooden member 148 with a vertically mounted 8 mm diameter tube 150. To conduct the flexibility test the second movable vertical member was manually moved with the vertical 8 mm diameter tube against the sample 152 held at a 0 degree position by the third arm until fracture occurred. The flexibility of the Al₂TiO₅ ceramic membrane separator test sample 152 can be seen in FIG. 46. The angle of fracture for classic ceramics is less than 1 degree, while FIG. 46 illustrates a 25 degree flexure for the Al₂TiO₅ material formed in accordance with the procedures described herein. This significantly increased flexibility has never been reported in the literature for any itacolumite type (microcrack hinge based) flexible material.

Statistically Designed Experiment to Determine the Control Variables for Sample Curling

A statistically designed experiment (Design of Experiment or DOE) was developed to determine the control variable responsible for the persistent problem of sample curling. It was found that the curling occurred during drying, although some additional curling caused by firing may have occurred as well. The DOE is shown in Table 9. The samples are ranked from 0 (no curling) to 5 (the worst curling). Samples were produced from a larger batch of Al₂TiO₅ slip (100316RW3091-2). Some samples were produced by dicing a nominal 1.5 in×1.5 in square, while others were stacks of alternating layers of 1.5 in×1.5 in squares of the cast dried slip. Samples were then pressed for various times and temperatures, as well as dried at various temperatures and times.

The commercial software package used to assist in planning and interpreting the DOE was Design Expert-Stat-Ease. A model for the correlation and response surfaces was developed that shows that there is less than a 0.0353 chance that the correlations and response surface are generated by random chance.

It was found that there is little, if any, effect on curling from either pressing time or drying time, within the ranges investigated. The control variables responsible for curling include: number of layers, pressing temperature, and drying temperature. This can be seen in FIGS. 47 and 48. Curling is minimized by using a large number of layers, higher pressing temperatures, and a lower drying temperature.

It has been concluded that tape squares larger than 1 inch×1 inch can be readily cast and fired using Al₂TiO₅ and larger sizes and different shapes can also be produced. Two examples of larger sized test samples (1.5 inch×1.5 inch square) are shown in FIG. 49. Based on these results, further improvements in size and physical properties can be readily obtained by optimizing tape formulations and slip processing, improved drying conditions, and using higher and better optimized firing temperatures. Scale-up of the slip size can be accomplished and separator materials of at least three (3) inch diameter circular separators can be produced.

TABLE 9 DESIGN OF EXPERIMENT (DOE) TO DETERMINE CONTROL VARIABLES FOR CURLING DUE TO DRYING B: C: D: E: A: PRESS- PRESS- DRY- DRY- DRY- No ING ING ING ING ING OF TEMP TIME TEMP TIME CURL- Std Run LAYERS C. min Klb h ING 7 1 1 150 10 20  2 0.5 1 2 1 100  3 90 16 4 4 3 4 150  3 90  2 0.5 5 4 1 100 10 90  2 4 6 5 4 100 10 20 16 0.5 2 6 4 100  3 20  2 1.5 3 7 1 150  3 20 16 0.5 8 8 4 150 10 90 16 0.5

CONCLUSION

The above and the attached Figures demonstrates the feasibility of producing an all-ceramic separator for use in lithium oxyhalide batteries (LOHB) to provide extended battery life. This decreases the frequency of battery replacement and, in turn, decreases costs, increases reliability, and increases the up-time for battery powered systems in remote or locations not easily accessed. Ceramic materials were developed that can be cast into green (unfired) tape from both 3YSZ and Al₂TiO₅ and drying protocols have been established to eliminate curling of the tapes during firing. The materials produced were testing for resistivity, corrosion, and ion permeability and demonstrated good results when compared with commercial separators. Specifically, 1.5×1.5 inch fired tape were cast from 3YSZ and Al₂TiO₅, fired tape from Al₂TiO₅ is sufficiently robust to allow for testing for ion permeability, and CeRollS formed from Al₂TiO₅ shows good DC resistivity, good corrosion resistance in thionyl chloride and sulfurylchloride, and better ion permeability than commercially available Celgard or ManniGlas Separators.

An all-ceramic separator that can perform in lithium oxyhalide batteries to extend the life of the battery has been demonstrated. This can decrease the frequency of battery replacement, thus decreasing costs, increasing reliability, and increasing the up-time for systems using lithium oxyhalide battery systems. Specifically, the ability to fabricate flexible films and/or tapes from ceramic materials with good resistivity and corrosion resistance for use in the harsh electrolytes typical of LOHBs, and having better ionic permeability compared to commercial separators, has been demonstrated.

The data herein demonstrates the ability to provide an innovative all-ceramic separator system. The materials developed can facilitate a replacement of commercial separators currently in lithium oxyhalide batteries which will avoid thermal and chemical breakdown and reduce the risk of fire and explosions. The performance characteristics of these materials meet or exceed the performance of commercial separator materials presently used lithium oxyhalide batteries in the areas of resistance to corrosion, electrical resistivity, and ion permeability. 

We claim:
 1. A substantially flat, flexible ceramic film comprising Yttria Stabilized Zirconia (3YSZ) or aluminum titanate (Al₂TiO₅), said ceramic film having a thickness from about 25-290 μm.
 2. The substantially flat, flexible ceramic film of claim 1, said film having physical properties suitable for use as a porous separator for use in electrical batteries.
 3. The flexible ceramic film of claim 2 comprising Al₂TiO₅ wherein said film separator has an ion permeability from about 1.1×10⁻¹⁵ to about 1.8×10⁻¹⁵ cm²/sec.
 4. The flexible ceramic film of claim 2 comprising Al₂TiO₅ wherein the physical properties of said ceramic film are inert to exposure to electrolytes.
 5. The flexible ceramic film of claim 4 wherein the electrolyte is selected from the group consisting of HCl, KOH, NaOH, LiCl, thionyl chloride, or sulfuryl chloride.
 6. The flexible ceramic film of claim 2 comprising Al₂TiO₅ wherein said film has pore sizes from about 0.5 to about 42 μm.
 7. The flexible ceramic film of claim 2 comprising Al₂TiO₅ wherein said film has an electrical resistivity of >5.4×10⁸ Ohm-cm.
 8. The flexible ceramic film of claim 2 comprising Al₂TiO₅ wherein said film has an ion permeability from about 1.1×10⁻¹⁵ to about 1.8×10⁻¹⁵ cm²/sec.
 9. The flexible ceramic film of claim 2 comprising Yttria Stabilized Zirconia wherein said film has an ion permeability from about 3.5×10⁻¹⁶ to about 6.2×10⁻¹⁶ cm²/sec.
 10. An electrical battery comprising layers of negative and a positive electrode materials, the layers of said negative and positive electrode materials spaced apart by one or more layers of a flexible Al₂TiO₅ or Yttria Stabilized Zirconia ceramic battery separator to form a layered structure with the positive electrode material connected to a positive current collector and the negative electrode material connected to a negative current collector to form a layered structure.
 11. The electrical battery of claim 9 wherein the layered structure is formed into a rolled structure.
 12. The electrical battery of claim 9 comprising a lithium oxidyhalide battery.
 13. A method of forming a flexible Al₂TiO₅ ceramic battery separator comprising: a. casting a film of ceramic particles in combination with a fugitive organic binder, said particles in a first instance a final size after milling ranging from 15-30 μm and in a second instance a final size after milling from 5-20 μm to form a tape, b. drying the tape at ambient temperature with Relative humidity (RH) ranging from 30-60% c. pressing of about 0-3 Klb at about 25-52° C., d. placing the dry tape on an inert substrate and heating the dry tape in air at least 1500° C. for at least 8 hours to form a fired tape, and e. cooling the fired tape to room temperature over a period of 2-12 hours
 14. The method of claim 11 further including applying pressure to the dry tape during the heating process. 